A planet where it is well known that people frequently switch between a variety of parallel universes... Koyomi Hidaka meets Shiori Satou in the research facility where his father works. Koyomi Hidaka, whose parents divorced, now resides with his father. They each have a small crush on one another, but when their parents remarry, everything changes. Koyomi and Shiori attempt to enter a different reality where they won't be step-siblings since they are convinced that they will never be together. Without her, the world is without purpose.